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International Mathematical Olympiad 2012 — Official contest Question 1

IMO · International Mathematical Olympiad 2012 — Official contest

Question 1

Let $ABC$ be a triangle and $J$ the center of the $A$-excircle. This excircle is tangent to the side $BC$ at $M$, and to the lines $AB$ and $AC$ at $K$ and $L$, respectively. The lines $LM$ and $BJ$ meet at $F$, and the lines $KM$ and $CJ$ meet at $G$. Let $S$ be the point of intersection of the lines $AF$ and $BC$, and let $T$ be the point of intersection of the lines $AG$ and $BC$. Prove that $M$ is the midpoint of $\overline{ST}$.